In continuous casting of an ingot, titanium or a titanium alloy melted by heating the melt surface by plasma arc melting (PAM) or electron beam melting (EB) is charged into a bottomless mold and pulled out downward while solidifying it.
Patent Document 1 discloses an automatically controlled plasma melting casting method. In the automatically controlled plasma melting casting method, titanium or a titanium alloy is melted by plasma arc in an inert gas atmosphere, charged into a mold, and solidified. Unlike electron beam melting that is performed in vacuum, the plasma arc melting method performed in an inert gas atmosphere described in Patent Document 1 can cast not only pure titanium but also a titanium alloy.
Patent Document 2 discloses an apparatus for melting and continuous casting a high-melting-point metal ingot by an electron beam method. In the melting and continuous casting apparatus descried in Patent Document 2, an ingot is pulled out while rotating its bottom, and among electron beams for irradiation, the melt surface is irradiated while making the density of electron beams incident along the peripheral part of a mold be higher than that in the central part of the mold.
Since the ingot formed of titanium or a titanium alloy is completed as a product through steps of rolling, forging, heat treatment, etc., an ingot having as a large diameter as 800 to 1,200 mm is required for obtaining a product excellent in the mechanical properties such as fatigue strength.